I kill any spider I see if it's inside my house, preferably with a long object like a rolled up newspaper, fly swatter, or katana (it was the most convenient thing at the time.) I'm not so squeamish about things like moths, which I'll grab out of the air and squish in my fist. I don't like bugs. I think there is a genetic reason for arachnophobia, since someone mentioned it. Apparently a long-gone ancestor of humans was mortally threatened by the predecessor of today's spiders, making paranoid and cautious (sometimes almost paralytic) behavior around spiders for some of our evolutionary history a favorable but not universal trait. It isn't a big deal anymore, so it's no longer selected for and some people have it while others don't. I only mind large spiders, littler ones I'll still kill though. Yellow jackets are somewhat of an exception, I've even (successfully) encouraged a few to land on my hand for a little while. But spiders? They give me the willies. They oughtn't just as far as rationality, but they do. It has to be something about my lower brain that causes that, and that would be something genetic.